<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>demo1</title>
</head>

<body>
  <div id="root"></div>
  <script>
    const rootElement = document.getElementById("root");
    const ele = document.createElement("div");
    ele.textContent = "Hello world!";
    ele.className = "hello "
    rootElement.appendChild(ele);
  </script>
</body>

</html>